Photoelectric conversion elements are used in various photosensors, copying machines, solar cells or the like. These photoelectric conversion elements have adopted various systems to be put into use, such as elements utilizing metals, elements utilizing semiconductors, elements utilizing organic pigments or dyes, or elements utilizing combinations of these. In particular, solar cells that make use of non-exhaustive solar energy do not necessitate fuels, and full-fledged practicalization of solar cells as an inexhaustible clean energy is being highly expected. Above all, research and development of silicon-based solar cells have long been in progress. Based on a policy-wise consideration in each country, widespread use thereof is still in progress. However, silicon is an inorganic material, and has its own limitations in terms of improving throughput and cost.
Under such circumstances, research is being vigorously carried out on dye-sensitized solar cells. Especially, to have built momentum toward such research is research results by Graetzel et al. of École Polytechnique Fédérale de Lausanne in Switzerland. They employed a structure in which a dye formed from a ruthenium complex was fixed at the surface of a porous titanium oxide thin film, and realized a photoelectric conversion efficiency that was comparable to that of amorphous silicon. Thus, the dye-sensitized solar cells that can be produced even without using an expensive vacuum apparatus instantly attracted the attention of researchers all over the world.
Hitherto, as metal complex dyes to be used in photoelectric conversion elements, dyes generally called as N3, N719, Z907, and J2 have been developed.
On the other hand, investigations on the adsorptive group to the surface of semiconductor fine particles in terms of the kind and introduction method thereof have been conducted in order to utilize the light in the wavelength region of 800 nm or more or the light having a wavelength in the visible or infrared region. There were proposals that an adsorptive group such as acidic group be introduced to a pyridine ring via an ethenylene group (see Patent Literature 1) and that an ethenyl group substituted with an acidic group and a specific electron withdrawing group at the 2-position be bonded to the chromophore via a conjugated system (see Patent Literature 2). However, these proposals were not entirely satisfactory for an improvement in the photoelectric conversion efficiency and durability.